Fish persistence and fluvial geomorphology in central Australia     

Peter J. Unmack 《Journal of Arid Environments》2001,49(4):653

The purposes of this paper are to document the composition and distribution of fishes in the Alice Springs region of Australia, and discuss constraints on fish persistence in this arid region. Nine native and six exotic species were recorded; most exotics no longer exist. Except in Finke River, only one or no native species were found. Fish survival in the area is ameliorated by the exceptionally broad environmental tolerances and migratory abilities of many species, but ultimately depends upon the effects of geology, geomorphology, and the vagaries in pattern of sediment transport on water persistence.  相似文献   

From small scales to the big picture: persistence mechanisms of planktonic grazers in the oligotrophic ocean   总被引：1，自引：0，他引：1  

Gustav-Adolf Paffenhöfer  Barry F. Sherr  & Evelyn B. Sherr 《Marine Ecology》2007,28(2):243-253

In this review we evaluate whether universal behavioral and metabolic mechanisms exist, which permit marine proto‐ and metazooplankton to persist in continuously food‐limited environments such as the North Pacific Subtropical Gyre and other oligotrophic ocean systems. We re‐visit the issue of what processes account for low steady‐state abundance of the dominant groups of planktonic grazers: phagotrophic protists and copepods, by examining evidence for the four processes proposed by Strom et al. (2000) : grazing thresholds, behavioral response to prey patchiness, top–down control of grazers, and mixotrophy (combination of photosynthesis and phagotrophy in protists) and/or omnivory (switching between alternate prey types). Published observations reveal that grazing thresholds, below which feeders reduce their feeding efforts and, with that, their metabolic expenditures, do exist. There are also studies suggesting that both protistan and small metazoan plankton feeders may take advantage of patchiness of food particles and are frequently mixotrophic and/or omnivorous. Predator patchiness in response to prey patches may facilitate top–down control of grazers. Finally, we discuss processes, which may lead to low quasi steady‐state abundances of food particles and feeders.  相似文献   

A general Bayesian framework for calibrating and evaluating stochastic models of annual multi-site hydrological data   总被引：1，自引：0，他引：1  

Andrew J. Frost  Mark A. Thyer  R. Srikanthan  George Kuczera 《Journal of Hydrology》2007,340(3-4):129-148

Multi-site simulation of hydrological data are required for drought risk assessment of large multi-reservoir water supply systems. In this paper, a general Bayesian framework is presented for the calibration and evaluation of multi-site hydrological data at annual timescales. Models included within this framework are the hidden Markov model (HMM) and the widely used lag-1 autoregressive (AR(1)) model. These models are extended by the inclusion of a Box–Cox transformation and a spatial correlation function in a multi-site setting. Parameter uncertainty is evaluated using Markov chain Monte Carlo techniques. Models are evaluated by their ability to reproduce a range of important extreme statistics and compared using Bayesian model selection techniques which evaluate model probabilities. The case study, using multi-site annual rainfall data situated within catchments which contribute to Sydney’s main water supply, provided the following results: Firstly, in terms of model probabilities and diagnostics, the inclusion of the Box–Cox transformation was preferred. Secondly the AR(1) and HMM performed similarly, while some other proposed AR(1)/HMM models with regionally pooled parameters had greater posterior probability than these two models. The practical significance of parameter and model uncertainty was illustrated using a case study involving drought security analysis for urban water supply. It was shown that ignoring parameter uncertainty resulted in a significant overestimate of reservoir yield and an underestimation of system vulnerability to severe drought.  相似文献   

The behaviour of the mean energetic level in time and space: Persistence,autocorrelations, links to standard levels     

Radan Huth 《Studia Geophysica et Geodaetica》1995,39(4):449-465

Summary The variances, persistence, and spatial autocorrelations of the basic quantities at the mean energetic level (MEL) as well as the links between the MEL and standard isobaric levels are investigated. The statistics obtained for the MEL are compared with those for height and temperature at the 500 and 300 hPa levels. The behaviour of most quantities at the MEL does not show any peculiarity making it substantially different from isobaric levels. The only quantity at the MEL, not closely correlated with any variable at adjacent standard levels, appeared to be the pressure.  相似文献   

Persistence of benthic communities: a case study from the Valli di Comacchio, a Northern Adriatic lagoonal ecosystem (Italy)   总被引：1，自引：0，他引：1  

Mistri  Michele 《ICES Journal of Marine Science》2002,59(2):314-322

  相似文献   

拱坝坝肩侧裂面的面连通率研究   总被引：2，自引：0，他引：2  

王良奎  陈剑平  卢波 《煤田地质与勘探》2002,30(1):41-44

采用窗口法对拱坝坝肩不连续面进行描绘测量,对获取的不连续面的产状和迹长进行取样偏差校正和蒙特卡罗模拟,从而形咸三维空间的不连续面网络模型。据工程要求对网络模型按一定带宽进行切割、投影、计算,由此可得到侧裂结构面的面连通率。在此基础上,可以进行坝肩岩体质量评价,为工程设计提供一定的理论依据。   相似文献   

The role of barrier layer in southeastern Arabian Sea during the development of positive Indian Ocean Dipole events   总被引：1，自引：0，他引：1  

Feiyan Guo  Qinyu Liu  Xiao-Tong Zheng  Shan Sun 《中国海洋大学学报(英文版)》2013,12(2):245-252

Using data from Argo and simple ocean data assimilation (SODA), the role of the barrier layer (BL) in the southeastern Arabian Sea (SEAS: 60°E–75°E, 0°–10°N) is investigated during the development of positive Indian Ocean Dipole (IOD) events from 1960 to 2008. It is found that warmer sea surface temperature (SST) in the northern Indian Ocean appears in June in the SEAS. This warm SST accompanying anomalous southeastern wind persists for six months and a thicker BL and a corresponding thinner mixed layer in the SEAS contribute to the SST warming during the IOD formation period. The excessive precipitation during this period helps to form a thicker BL and a thinner mixed layer, resulting in a higher SST in the SEAS. Warm SST in the SEAS and cold SST to the southeast of the SEAS intensify the southeasterly anomaly in the tropical Indian Ocean, which transports more moisture to the SEAS, and then induces more precipitation there. The ocean-atmosphere interaction process among wind, precipitation, BL and SST is very important for the anomalous warming in the SEAS during the development of positive IOD events.  相似文献   

中国区域干旱的持续性特征研究     

李忆平  王劲松  李耀辉  王素萍  沙莎 《冰川冻土》2014,36(5):1131-1142

利用1961-2012年中国区域586个气象站的降水、气温、日照时数、相对湿度、风速等资料计算了逐月K干旱指数, 在此基础上, 对全国16个区的干旱持续性特征进行了研究. 结果表明: 华北、河套、西北地区东部、西南地区北部、黄淮及新疆南部地区干旱的持续性较强, 常发生3个月以上的长期干旱过程, 并且容易在旱情解除后的短期内(1个月)再次出现干旱; 而南方、东北和新疆北部地区干旱的持续性较弱, 以1个月的短期干旱为主, 且干旱过程之间的时间间隔相对较长, 大多为3个月以上; 华北、河套、西北地区东部、西南地区北部和南部、以及华南地区的干旱过程在冬、秋季开始的频次最高, 且大部分在春季结束, 而冬、春两季的干旱明显比夏、秋两季偏多. 100°E以西(新疆北部除外)的广大地区干旱过程的开始时间主要集中在秋季, 结束时间集中在春、冬两季; 同时, 冬季和秋季干旱多发, 其次是春季, 夏季出现的干旱频次最少.  相似文献   

The scientific legacy of Harold Edwin Hurst (1880–1978)     

P.E. O’Connell  D. Koutsoyiannis  H. F. Lins  Y. Markonis  A. Montanari  T. Cohn 《水文科学杂志》2016,61(9):1571-1590

ABSTRACT

Emanating from his remarkable characterization of long-term variability in geophysical records in the early 1950s, Hurst’s scientific legacy to hydrology and other disciplines is explored. A statistical explanation of the so-called “Hurst Phenomenon” did not emerge until 1968 when Mandelbrot and co-authors proposed fractional Gaussian noise based on the hypothesis of infinite memory. A vibrant hydrological literature ensued where alternative modelling representations were explored and debated, e.g. ARMA models, the Broken Line model, shifting mean models with no memory, FARIMA models, and Hurst-Kolmogorov dynamics, acknowledging a link with the work of Kolmogorov in 1940. The diffusion of Hurst’s work beyond hydrology is summarized by discipline and citations, showing that he arguably has the largest scientific footprint of any hydrologist in the last century. Its particular relevance to the modelling of long-term climatic variability in the era of climate change is discussed. Links to various long-term modes of variability in the climate system, driven by fluctuations in sea surface temperatures and ocean dynamics, are explored. Several issues related to the Hurst Phenomenon in hydrology remain as a challenge for future research.